Built-in hashers & comparers

This release adds built-in Hasher & Comparer types for all int & uint types (e.g. int, int8, int16, etc) as well as stringand[]byte`.

It also includes reflection-based hasher & comparers for int, uint, and string types that have been aliased . For example, reflection based hashers will be used for a type declared like this:

type ID int

Thanks to @adrianboyko for the reflection-based hashers! 🎉